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@HOPE2 wrote:

Around January 2024 he contributed on Roth 401-K and Solo401-K under his name for the year of 2024. (same description: 2024 employee contribution)

now I think he should cancel recent solo 401-K contribution under his name? Am I right?  

and run 401-k through the payroll because he wants to have a employee for 2024.

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Yes.  Any 401k contributions for 2024 need to be through the S-corporation and the employee portion is processed through payroll.